1. Field of the Invention
The invention relates generally to a light source and, more particularly, to a field emission light source for use in a backlight device.
2. Discussion of Related Art
The conventional artificial light sources include, for example, incandescent lamps, fluorescent lamps, light emitting diodes (LED), high-intensity discharge lamps (HID), incandescent lamps, and halogen lamps. An incandescent lamp uses a glowing wire filament to generate light and heat by electrical resistance. Because of its poor efficiency, incandescent lamps are generally used in household illumination and are gradually being replaced by fluorescent lights, high-intensity discharge lamps, LEDs, and other more efficient devices.
A fluorescent lamp is a type of lamp that uses electricity to excite mercury vapor in argon or neon gas, resulting in a plasma that produces short-wave ultraviolet light. This light then causes a phosphor to fluoresce, producing visible light. Fluorescent lamps are much more efficient than incandescent lamps of an equivalent brightness and have a longer lamp life, in part, because such lamps operate at a much lower working temperature. However, the use of mercury makes fluorescent lamps unaccommodating to the demands of environmental protection.
A light-emitting diode (LED) is a special type of semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction. LEDs are capable of emitting light of an intended color without the use of color filters that traditional lighting methods require. LEDs give off less heat than incandescent lamps and are less fragile than fluorescent lamps. Thus, LED-based light sources are generally used for household illumination and outdoor signals.
A high-intensity discharge (HID) lamp produces light by striking an electrical arc across tungsten electrodes housed inside a specially designed inner fused quartz or fused alumina tube. Compared to fluorescent and incandescent lamps, HID lamps produce a large quantity of light in a small package. So, HID lamps are typically used when high levels of light are required over large areas and when energy efficiency and/or long life are desired. However, the operation of HID lamps must withstand a high voltage up to 23,000 volts at the start of lighting and must maintain a voltage of 8,000 volts to provide a continuously steady lighting. Such lamps thereby require a special voltage-transforming device, which increases an overall size of the lighting device.
Referring to FIG. 5 (Prior Art), a light source using carbon nanotubes solves the above problems. The light source includes a metal film 510, a lower substrate 520, a conductive polymer film pattern 530, carbon nanotubes 540, a transparent upper substrate 550, a transparent electrode 560, and a fluorescent body 570. The metal film 510 is used as a cathode and is formed on the lower substrate 520. The conductive polymer film pattern 530 is formed on the metal film 510. The carbon nanotubes 540 are substantially vertically bound with the conductive polymer film pattern 530 such that one end thereof is exposed above the surface of the conductive polymer film pattern and such that the other end thereof is available for emitting electrons. The transparent upper substrate 550 has the transparent electrode 560 to which the fluorescent body 570 is attached. Further, the transparent electrode 560 is mounted on the spacers such that the fluorescent body 570 faces the carbon nanotubes 540. The white light source has an excellent electric field electron emission efficiency to thereby obtain a large emission current even at a low applied voltage and has a very high density of electron emitters per unit area to thereby exhibit excellent luminous efficacy.
However, the carbon nanotubes, used in the above light source for emitting electrons, are hollow. During the operation of the electron emission in the effect of the electric field, the carbon nanotubes are easily distorted, and therefore, the life span of such a white light source is short. Furthermore, because the carbon nanotubes are substantially vertically attached on the conductive polymer film pattern, another problem may result. Specifically, when the effect of the electric field is increased, the carbon nanotubes can possibly break away from the conductive polymer film pattern. Such separation can also decrease the life span of the white light source.
What is needed, therefore, is a light source having both field emission efficiency and a long life span.